The long-term goal of this project is to understand the mechanism of formation of subepithelial (SE) dense immune deposits found in the idiopathic membranous human glomerulonephritis. The rat Heymann nephritis (HN) has been an accepted animal model to study the pathogenesis of the SE deposits. It has been suggested that SE deposits may arise from immune complexes formed on the glomerular epithelial cell (GEC). This proposal is focused at studying the kinetics and fate of the HN related immune complexes formed on the GEC and the metabolic consequences which follow. Following specific issues will be addressed: I. To determine the kinetics of immune complex formation and the proportion of complexes shed and the proportion of complexes digested by the GEC using various Heymann nephritis related antibodies. Cultured cloned GEC will be used. Radioactive antibody tracing techniques and gel filtration chromatography will be employed. II. To separate the shed immune complex material into various molecular size species and characterize each of them for antigen and antibody content. Molecules will be separated by gel filtration techniques. Antigen, antibody will be detected by radioimmunoassay in each fraction. III. To study the cellular mechanisms by which the complexes are processed by the GE. EM autoradiography, immunoperoxidase and EM Protein A gold labelling techniques will be used. IV. To determine whether immune complex formation influences the later expression and presentation of the involved antigens. Immunoblot and radioimmunoprecipitation analysis on the cytosol and membrane fraction of the GEC will be employed to quantitate the in- volved antigens. V. To determine if immune complex formation alters the general metabolic state of GEC and leads to altered synthesis of extracellular matrix components such as collagen and SO4 containing proteoglycans (PG). Conversion of proline to hydroxyproline will be assayed for evaluation of collagen synthesis. Sulfated PG will be assayed by radioactive SO4 pulsing and separation of sulfated macromolecules on an ion exchange column. These studies will clarify the role of immune complex formation on the GEC in the pathogenesis of subepithelial deposits.